Propargyl bromide (3-bromopropyne) is known to be useful as a soil fumigant for control of fungi, nematodes, and undesirable plant life. See for example U.S. Pat. No. 2,794,727. For such usage it would be necessary to store and transport propargyl bromide from its manufacturing site to other locations and ultimately to farmlands where it would be put to use. And, in order to utilize propargyl bromide most effectively as a soil fumigant it would be desirable to have the ability to use it in pressurized dispensing systems wherein the pressurized fumigant is injected subsurface to the soil during cultivation.
Propargyl bromide is, however, a high energy material that is sensitive to physical shock or impact, and that is also susceptible to rapid thermal decomposition upon exposure to high temperatures or fires. In order to more safely produce, purify, store, transport, handle and use propargyl bromide, it is desired to stabilize the propargyl bromide against physical shock and exposure to elevated temperatures both in the liquid and vapor phase especially when in a confined space. In addition, since use of propargyl bromide as a soil fumigant would often involve having the product housed in pressurized systems or containers so that it can be injected into the soil, stabilization of propargyl bromide against physical shock and exposure to elevated temperatures when confined under pressure is another goal to be accomplished.
The hazardous character of propargyl bromide has been recognized heretofore, and certain stabilizing materials have been proposed for use. For example, as indicated in Brit. 1,132,417, propargyl bromide is shock sensitive, and when in a confined space, propargyl bromide may ignite spontaneously and decompose with explosive violence, and may detonate. To provide stabilization, Brit. 1,132,417 indicates that certain solvents were effective, namely toluene, xylene, a non-cyclic ether, tetrahydrofuran, dioxane, beta-ionone, and ethanol. Brit. 1,132,417 further points out that many organic liquids had been tried for the purpose of stabilizing propargyl bromide, but only a few had been successful, that no firm rule had been established for predetermining which liquids would be successful and which would not, and that among materials that were tested and found ineffective were hexane, benzene, chloroform, formamide, and light petroleum oil.
In a paper entitled xe2x80x9cExplosibility and Stabilization of Propargyl Bromidexe2x80x9d, Loss Prevention, 1967, 1, 6-9, it is noted that propargyl bromide is sensitive to both shock and to temperature, and that under suitable conditions may be detonated, and that stabilization by dilution was explored as a possible solution to this problem. The authors of this paper report that at a diluent level of 15%, benzene, formamide, chloroform and hexane were judged by impact tests to be poor stabilizers for propargyl bromide, and that diethyl ether and diisopropyl ether appeared promising but were considered less attractive than toluene, xylene, and ethylhexylsorbitol. Based on processing considerations and impact test results, toluene and xylene were selected by the authors of this paper for further testing. In confinement tests toluene was judged by them to be the material of choice, especially at a dilution level of 20-30%. At present, propargyl bromide diluted with 20% of toluene is available as an article of commerce.
Unfortunately, toluene and xylene are both incapable of effectively stabilizing propargyl bromide in the vapor state. Thus conditions could be encountered in which propargyl bromide in admixture with toluene might nonetheless undergo explosive decomposition. Also, in order to use propargyl bromide as a soil fumigant it is important to avoid contaminating the soil with materials that leave residues that are not readily broken down by naturally-occurring microorganisms in the soil. Aromatic hydrocarbons such as toluene and xylene are not environmentally friendly as they are not rapidly consumed by such naturally-occurring microorganisms.
Thus a need exists for a new, environmentally-friendly way of effectively stabilizing propargyl bromide against both shock-induced and rapid heat-induced decomposition when in the vapor state and in the liquid state, and especially when under confinement under pressure. Because of the hazardous characteristics of propargyl bromide this need exists at all stages of its existence, including production, recovery, purification, handling, storage, transportation, and use.
This invention enables fulfillment of this and other needs as well.
It has been found that propargyl bromide can be effectively stabilized by combining propargyl bromide with an environmentally-acceptable inert liquid solvent that forms an azeotrope with propargyl bromide, such as a paraffinic and/or cycloparaffinic hydrocarbon solvent that forms an azeotrope with propargyl bromide. By xe2x80x9cazeotropexe2x80x9d is meant a mixture that under temperature and pressure conditions encountered at any normal stage of the life-cycle of propargyl bromide, the propargyl bromide and a stabilizing amount of the hydrocarbon when in the liquid or vapor state remain together at all times. Thus the stabilization activity provided by the solvents used pursuant to this invention protects the propargyl bromide against hazardous shock-induced or thermally-induced decompositions whether the propargyl bromide is in the liquid state or in the vapor state. And accordingly, it is now possible to produce, recover, purify, handle, store, transport, and use propargyl bromide without fear of disastrous consequences, such as those resulting from rapid exothermic decomposition.
By xe2x80x9cenvironmentally-acceptablexe2x80x9d is meant that the inert liquid satisfies or, if not yet evaluated, will satisfy the requirements for listing as an xe2x80x9cinertxe2x80x9d or xe2x80x9cother ingredientsxe2x80x9d in categorized List 1, List 2, List 3, or List 4 of the Office of Pesticide Programs of the United States Environmental Protection Agency, such lists as updated Jun. 12, 2001. Such lists are incorporated herein by reference as if fully set forth herein, except that all substances on such lists which do not meet all criteria specified herein are excluded from such lists because they are incapable or unsuitable for use in the practice of this invention.
Another embodiment of this invention is a closed container such as a drum, tank, tank car, tank trailer, or the like containing (i) a solution comprising propargyl bromide and a solvent that is compatible with propargyl bromide, and (ii) a headspace or vapor space within said container, wherein said headspace or vapor space contains an inert gas such that the headspace or vapor space is devoid or substantially devoid of air and elemental oxygen. The solvent in this embodiment of the invention can be any solvent such as those described in Brit. 1,132,417, in the above paper entitled xe2x80x9cExplosibility and Stabilization of Propargyl Bromidexe2x80x9d, Loss Prevention, 1967, 1, 6-9, or U.S. Pat. No. 2,794,727, such as toluene or zylene, but preferably is an environmentally-acceptable inert liquid solvent that forms an azeotrope with propargyl bromide. More preferably, the solvent results in the composition being classifiable as a xe2x80x9cflammable liquidxe2x80x9d, in accordance with Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 3rd Revised Edition, published by United Nations, New York and Geneva, 1999 (ISBN 92-1-139068-0).
The various embodiments of this invention will be still further apparent from the ensuing description and appended claims.
This invention enables propargyl bromide to be protected from the moment of its creation until the moment of its ultimate consumption, provided the material does not encounter some extraordinary set of conditions along the way. And even if the propargyl bromide encounters a dangerous condition such as a fire during storage or transportation, a collision during transportation, or excessive heat and pressure buildup during confinement, the severity and force of the decomposition of the propargyl bromide is greatly reduced.
Preferred compositions comprise a mixture of propargyl bromide, an inert liquid azeotropic solvent, and (i) a free radical inhibitor such as a sterically-hindered phenolic compound. Such compositions have been found to possess the additional advantage of resisting chemical transformation, e.g., chemical rearrangement to bromoallene, which can slowly occur during long periods of storage at ambient temperatures. As used herein xe2x80x9cazeotropicxe2x80x9d means that the solvent dissolves in propargyl bromide and forms an azeotrope with propargyl bromide so that a stabilizing amount of the solvent remains associated with the propargyl bromide at all times in both in the liquid state and in the vapor state.
Another group of preferred compositions comprise a mixture of propargyl bromide, an inert liquid azeotropic solvent, and an acid scavenger, such as epoxidized soybean oil. These compositions retain the excellent stability characteristics provided by the azeotropic solvent, and additionally are resistant to formation of color bodies and acid contaminants in the product.
Also preferred are compositions which comprise a mixture of propargyl bromide, an inert liquid azeotropic solvent, a free radical inhibitor such as a sterically-hindered phenolic compound, and an acid scavenger, such as epoxidized soybean oil. These compositions retain the excellent stability characteristics provided by the azeotropic solvent, resist chemical transformation, e.g., chemical rearrangement to bromoallene, and resist formation of color bodies and acid contaminants in the product.
Pursuant to preferred embodiments of this invention, there is provided a process of preparing propargyl bromide, which process comprises reacting in a reaction zone phosphorus tribromide and propargyl alcohol in an inert liquid azeotropic solvent that forms an azeotrope with propargyl bromide, to form a reaction mass containing propargyl bromide and said azeotropic solvent, and separating a mixture consisting essentially of propargyl bromide and said azeotropic solvent from the reaction mass, whereby a stabilizing amount of said azeotropic solvent is present with the propargyl bromide both in the liquid state and in the vapor phase (i) during the time the propargyl bromide is being formed and (ii) during and after the time propargyl bromide is being separated from the reaction mass. Preferably, the separated mixture of propargyl bromide and said azeotropic solvent is subjected to purification and optionally but preferably, to subsequent formulation with at least one other additive component, whereby propargyl bromide and a stabilizing amount of said azeotropic solvent remain together both in the liquid state and in the vapor phase at all times during the purification and the subsequent formulation operations. The resultant composition, whether or not subjected to the subsequent formulation, can then be packaged, stored, transported and used, whereby propargyl bromide and a stabilizing amount of said azeotropic solvent remain together both in the liquid state and in the vapor phase at all times during any and all such packaging, storage, transport and/or use. Preferably, a formulation step is carried out using (i) a free radical inhibitor such as a sterically-hindered phenolic compound, or (ii) an acid scavenger, such as epoxidized soybean oil, or both of (i) and (ii).
The term xe2x80x9cinertxe2x80x9d as used herein means that the solvent does not chemically react with the reactants used in producing the propargyl bromide under the conditions used for producing the propargyl bromide, and does not react with the propargyl bromide during the conditions used for producing the propargyl bromide or during normal conditions encountered during the recovery, purification, handling, storage, transportation, or use of the propargyl bromide.
By the term xe2x80x9cstabilizing amountxe2x80x9d with reference to the inert azeotropic solvent is meant an amount of the inert azeotropic solvent that is at least sufficient to provide a propargyl bromide composition that, if and when subjected in liquid form to the Bundesanstalt fur Materialprufung (BAM) Impact Test procedure as described in Example 5 hereinafter, exhibits no decomposition in any of 10 replicate tests. Although some azeotropic solvents are effective at even lower amounts, typically the minimum stabilizing amount of the azeotropic solvent combined with the propargyl bromide will be at least about 10 wt % of the composition. Preferably, the amount used should be at least about 15 wt % and more preferably at least about 20 wt % to provide a greater margin of safety. As a practical matter, the stabilized propargyl bromide product in the liquid state will normally not contain more than about 50 wt %, and preferably not more than about 35 wt %, of the azeotropic solvent. Preferably, the composition when in the vapor state exists at atmospheric pressure as a composition containing at least about 10 wt %, preferably at least about 15 wt %, and more preferably at least about 20 wt % of the solvent.
Still another embodiment of this invention is a method of controlling at least one pest selected from nematodes, fungi, and undesired plantlike, which method comprises applying to said at least one pest or to the locus thereof, or to both said at least one pest and the locus thereof, a mixture comprised of propargyl bromide and an inert liquid azeotropic solvent. Such mixture optionally but preferably is further comprised of (i) a free radical inhibitor such as a sterically-hindered phenolic compound, or (ii) an acid scavenger, such as epoxidized soybean oil, or both of (i) and (ii).
In preferred embodiments of this invention, the propargyl bromide composition meets the requirements for classification as a xe2x80x9cflammable liquidxe2x80x9d. In this connection attention is invited to Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 3rd Revised Edition, published by United Nations, New York and Geneva, 1999 (ISBN 92-1-139068-0).
Various azeotropic solvents can be used in the practice of this invention. Non-limiting examples include n-heptane, mixed heptane isomers, cyclohexane, methylcyclohexane, 2-methylhexane, 2,4-dimethylpentane, n-octane, isooctane, 2-methylheptane, 2,2-dimethylhexane, isopropyl alcohol, and a mixture of cyclohexane and isopropyl alcohol. A preferred solvent mixture is composed of a mixture of C7-9 hydrocarbons (e.g., Isopar E, ExxonMobil Chemical Corporation) in admixture with cyclohexane. A particularly preferred azeotropic solvent is a mixture composed primarily of C8 isoparaffinic hydrocarbons such as Isopar C (ExxonMobil Chemical Corporation).
As noted above, it is preferred to include an epoxide, preferably an epoxidized oil such as expoxidized soybean oil as a component of the compositions of this invention. It is also particularly preferred to further include a small amount of a hindered phenol such as 4-methyl-2,6-ditertbutyl phenol. Especially preferred mixtures are composed of about 60-70 wt % (e.g., 67.5 wt %) of propargyl bromide, about 30-35 wt % (e.g., 31 wt %) of Isopar C, about 0.5-5 wt % (e.g., 1 wt %) of epoxidized soybean oil, and about 0.05-0.7 wt % (e.g., 0.5 wt %) of 4-methyl-2,6-ditertbutyl phenol.
An additional and preferred option for any of the compositions of this invention is the presence of an inert gas such as nitrogen, helium, or argon. This minimizes or excludes oxygen from the composition, and usually results in a further decrease of the shock sensitivity of the propargyl bromide composition. For example, it has been discovered that adiabatic decomposition resulting from severe impact of propargyl bromide when in a confined space can be avoided by filling the head space above the liquid with an inert gas. Nitrogen is a preferred inert gas. The inert gas can be introduced into the composition by various means, such as blanketing the composition with an inert gas during its production, separation, and blending operations, and keeping it in a closed container under an inert atmosphere during storage and transportation.
It is advantageous to include an antioxidant (which is typically a free radical scavenger) in the composition of propargyl bromide to minimize isomerization of the propargyl bromide. Antioxidants or free radical scavengers that can be used with propargyl bromide include phenolic antioxidants, arylphosphites, and amines. Suitable phenolic antioxidants are typically sterically hindered phenolic antioxidants. Such antioxidants include, but are not limited to, 2-tert-butylphenol, 2-tert-amylphenol, 2,6-diisopropylphenol, 4-methyl-2-tert-butylphenol, 2,4-di-tert-butylphenol, 2,4-di-tert-butyl-5-methylphenol, 2,4-di-tert-butyl-6-methylphenol, 2,6-di-tert-butyl-4-methylphenol (also called BHT), 3,4-dimethyl-6-tert-butylphenol, 3,6-di-tert-butyl-4-(2-methylbutyl)phenol, 2,4,6-tri-tert-butylphenol, 4-tert-butylcatechol, 3-tert-butylresorcinol, methylenebis(2,6-di-tert-butylphenol), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and 2,5-di-tert-butylhydroquinone. Examples of arylphosphites that can be used are triphenylphosphite, tritolylphosphite, di(phenyl)(tolyl)phosphite, di(tolyl)(phenyl)phosphite, tri(naphthyl)phosphite, and tri(xylyl)phosphite. Amines that can be used as free radical scavengers which can be used are typically sterically-hindered amines. Preferred free radical scavengers are sterically hindered phenolic antioxidants. Highly preferred phenolic antioxidants are those that are U.S. Food and Drug Administration (FDA) approved, particularly when the composition is to be used for soil fumigation. Preferred hindered phenolic antioxidants are 2,6-di-tert-butylphenol, methylenebis(2,6-di-tert-butylphenol), and 2,6-di-tert-butyl-4-methylphenol; most preferred is 2,6-di-tert-butyl-4-methylphenol. Two or more different free radical scavengers may be used in a composition of the invention.
Acid scavengers in the composition prevent further reaction of acid decomposition products of propargyl bromide. Suitable types of acid scavengers include epoxides and epoxidized olefinically unsaturated oils. Examples of epoxides that can be used include, but are not limited to, 1,2-epoxypropane, 1,2-epoxybutane, 2,3-epoxybutane, 1,2-epoxyhexane, 1,2-epoxycyclohexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxydecane, 1,2-epoxycyclododecane, and styrene oxide. Epoxidized olefinically unsaturated oils that can be used include epoxidized babassu oil, epoxidized palm oil, epoxidized olive oil, epoxidized peanut oil, epoxidized rapeseed oil, epoxidized corn oil, epoxidized sesame oil, epoxidized cottonseed oil, epoxidized sunflower oil, epoxidized safflour oil, epoxidized hemp oil, epoxidized linseed oil, epoxidized lard oil, epoxidized neat""s foot oil, and the like. Epoxidized olefinically unsaturated oils are preferred acid scavengers. Preferred is epoxidized soybean oil. Two or more acid scavengers can be used in a composition of the invention.
In the process of preparing propargyl bromide pursuant to this invention, propargyl alcohol, phosphorus tribromide, a stabilizing agent A) or B), optionally with a previously known stabilizing agent, such as toluene, and an amine catalyst are components of the reaction mixture. A reaction zone is formed at any point at which propargyl alcohol and phosphorus tribromide are brought into contact. This can result in the components coming together outside of a typical reactor or reaction vessel. The reaction zone usually may be any of a variety of reactors or mixers. The reaction components can initially be brought into contact with each other in a mixing device in proximity to, but apart from, a reactor or reaction vessel. Suitable mixing devices include a static mixer, a conduit (preferably a conduit in which there is turbulent flow), or a jet mixer that produces a high velocity effluent stream. In all such cases, the mixing device itself in which propargyl alcohol and phosphorus tribromide first come into contact with each other is part of the reaction zone. Preferably, the reactants are concurrently fed into a reaction zone composed of at least one reactor or mixer in which all of the componentsxe2x80x94whether fed individually or in any subcombination(s)xe2x80x94all come together for the first time and in which the reaction to form propargyl bromide is initiated and carried out.
After the process of preparing propargyl bromide has been completed, at least one antioxidant and/or at least one acid scavenger may be added to the mixture.
For the process of preparing propargyl bromide, stabilizing agent A) and stabilizing agent B) are as described above for the propargyl bromide compositions. Preferred saturated hydrocarbons and amounts are also as detailed above. Small amounts of toluene, one more xylene isomers, or a mixture of any of these, may be present in the stabilizing agent. Preferred saturated hydrocarbons and amounts for stabilizing agents A) and B) are as detailed above for the compositions.
The amine catalyst used in the process is normally a trihydrocarbyl amine. Amines that can be used as catalysts in a process of this invention include triethylamine, tributylamine, triphenylamine, tricyclohexylamine, and the like. Preferred amines are trialkylamines having up to 4 carbon atoms per alkyl group.
The process is normally conducted at one or more temperatures in the range of about to 10 about 80xc2x0 C. More preferably, the reaction is conducted in the range of about to 20 about 70xc2x0 C.; most preferably, the temperature is in the range of about to 25 about 60xc2x0 C. during the process of the invention.
It has been found possible to achieve still further advantages in connection with the manner in which the processes of the invention are carried out. More particularly, by cofeeding the reaction components, including the stabilizing agent, into the reactor or reaction zone, substantial additional advantages are obtained. The advantages of such cofeeding of the reaction components are that the temperature increase which happens during the reaction occurs more slowly, and that the temperature does not rise to as high a value as it does when phosphorus tribromide is added to a propargyl alcohol solution containing amine catalyst. This in turn is less demanding on cooling equipment. Typical high temperatures for a cofeed operation when adding phosphorus tribromide to a propargyl alcohol solution containing amine catalyst are about 40xc2x0 C. to about 70xc2x0 C.
When conducting a cofeed operation, the components should be fed so that the propargyl alcohol and the phosphorus tribromide contact each other in the presence of stabilizing agent. These components may be fed separately, or the agent may be fed in combination with the propargyl alcohol, the phosphorus tribromide, or in combination with both. Propargyl alcohol and phosphorus tribromide should not be fed together as the same feed. The amine catalyst may be co-fed singly, with agent, with propargyl alcohol, with phosphorus tribromide, or with any two or more of the other feeds. Cofeeding does not have an adverse effect on the yield of propargyl bromide (as compared to yields obtained when feeding phosphorus tribromide to a propargyl alcohol solution containing amine catalyst).
Each of the various feeds in the cofeed operation may be continuous or intermittent. Further, there is no requirement that any of the feeds occur simultaneously with any of the other feeds. For example, the separate feeds need not start or end at precisely the same time. Instead, there can be a suitably short time between the start of one feed and another, while still realizing the advantages of the cofeed operation. The point here is that the duration of the cofeeds should be sufficient to obtain the foregoing advantages, but need not be exactly coextensive in time.
For a cofeed operation, stabilizing agent A) and stabilizing agent B) are as described above for the process of preparing propargyl bromide. Preferred saturated hydrocarbons and amounts are also as detailed above. Small amounts of toluene, one more xylene isomers, one or more non-cyclic ethers, tetrahydrofuran, dioxane, beta-ionone, ethanol, or a mixture of any of these, may be present in the stabilizing agent. Although less preferred, toluene, one more xylene isomers, one or more non-cyclic ethers, tetrahydrofuran, dioxane, beta-ionone, ethanol, or a mixture of any of these may be used as the stabilizing agent for the cofeed operation.
When distilling propargyl bromide from the crude reaction product, use of a stabilizing agent having a boiling point similar to that of propargyl bromide is desirable because the stabilizing agent distills with the propargyl bromide. The presence of stabilizing agent in the vapor phase with propargyl bromide minimizes the shock sensitivity of propargyl bromide in the vapor phase. When a mixture of two or more saturated hydrocarbons is used, at least one of which has a boiling point lower than that of propargyl bromide and at least one of which has a boiling point higher than that of propargyl bromide, it is usually necessary to add more of the lower-boiling hydrocarbon(s) during distillation of propargyl bromide so that the lower-boiling hydrocarbon(s) does not become depleted from the mixture. Without being bound by theory, it is believed that saturated hydrocarbons form azeotropes with propargyl bromide, which causes such agent to always be present with the propargyl bromide whenever it vaporizes. The concentration of propargyl bromide would thus never increase above the azeotrope concentration, rendering the distillation inherently safe.